Imperative Lambda Calculus is a type system designed to combine functional and imperative programming features in an orthogonal fashion without compromising the algebraic properties of functions. It has been noted that the original system is too restrictive and lacks the subject reduction property. We define a revised type system that solves these problems using ideas from Reynolds's Syntactic Control of Interference. We also extend it to handle Hindley-Milner style polymorphism and devise type reconstruction algorithms. A sophisticated constraint language is designed to formulate principal types for terms. 1 Introduction The recent research in programming languages has greatly clarified the interaction between imperative and functional programming. The conventional notion that functional programming and imperative state-manipulation are in conflict has been dispelled. Several programming languages have now been designed which combine functions and assignments without destroying algeb...

Syntactic Control of Interference (SCI) [17] has long been studied asabasis for interference-free programming, with cleaner reasoning properties and semantics than traditional imperative languages. This paper improves upon Huang and Reddy's type inference system [7] for SCI-based languages in two signi cant ways. First, we eliminate the need for explicit coercion operators in terms. Second, we consider adding let-bound polymorphism, which appears to be nontrivial in the presence of interference control. SCI can be adapted to a wide variety of languages, and our techniques should be applicable to any such language with SCI-based interference control. 1

Syntactic Control of Interference (SCI) [Rey78] has long been studied as a basis for interferencefree programming, with cleaner reasoning properties and semantics than traditional imperative languages. This paper makes SCI-based languages more practical by introducing a revised version of Huang and Reddy's type reconstruction system [HR96] with two significant improvements. First, we eliminate the need for explicit coercion operators in terms. Although this can lead to more complex principal typings, we introduce some minor restrictions on the inference system to keep the typings manageable. Second, we consider adding let-bound polymorphism. Such a modification appears to be nontrivial. We propose a new approach which addresses issues of both polymorphism and interference control. Some examples show the utility of our system. SCI can be adapted to a wide variety of languages, and our techniques should be applicable to any such language with SCI-based interference control. 1 Introducti...